Antibiotic development has traditionally focused on drugs that target the pathogen but resistance inevitably develops. An attractive alternative is to develop drugs that target the host response and in particular for facultative/obligate intracellular bacterial pathogens, which rely on the host for disease progression. Intracellular bacterial pathogens manipulate the host cytoskeletal system to their advantage during various stages in infection. In particular a number of medically important pathogens activate the MEK-ERK cascade, which is known to be important in cytoskeletal dynamics. FDA-approved inhibitors of MEK are available but their efficacy is limited by their toxicity. We discovered and developed a specific small molecule inhibitor for RSK1/2, a downstream effector of the MEK-ERK signaling pathway. In preliminary experiments, using Yersinia pseudotuberculosis as a model intracellular bacterial system, we identified that RSK1/2 inhibition reduced the number of viable bacteria in infected macrophages, which correlated with inhibition of Y. pseudotuberculosis-induced cytoskeletal rearrangement. Furthermore, bacterial infection can result in sepsis, which results in a loss of epithelial integrity. Importantly, we identified that RSK2 regulates a gene signature enriched in immune response signaling in epithelial cells, suggesting that a RSK1/2 inhibitor will dampen the epithelial generated immune response and thereby, protect epithelial integrity. In support of these data inhibiting MEK signaling pathway was found to decrease organ dysfunction. For the phase I program, Blue Ridge Biosciences, LLC, a reagent discovery and development company, in collaboration with Vanderbilt University Medical Center, will assess the feasibility of targeting RSK1/2 as a drug target for facultative/obligate intracellular bacterial pathogens that activate the MEK-ERK pathway. Francisella tularenis will be used as proof-of-principle. The Specific Aims are (1) determine whether RSK1/2 limits propagation of F. tularenis in primary macrophages in vitro; (2) determine whether inhibition of RSK1/2 protects the integrity and viability of lung epithelial cells in vitro: and (3) test whether inhibition of RSK1/2 using a RSK1/2 knockout mouse model will ameliorate infection by F. tularenis in vivo. Data generated in this proposal will be analyzed using the appropriate statistics for end point and longitudinal analysis. These data will be used to support a phase II for the continued development of a RSK1/2 inhibitor as a novel strategy for combating infection.